The bacterium Myxococcus xanthus is a useful model system for the study of the mechanisms involved in the formation of multicellular structures. During M. xanthus development hundreds of thousands of cells aggregate to form mounds and individual cells within the mounds differentiate to form myxospores. These activities require communication between cells and synchronization of cellular functions, which are surely important aspects of the biology of any multicellular organism. One mechanism involved in the control of M. xanthus development is regulation of gene expression. To understand how genes are regulated in this system the proposed research focuses on expression of the development-specific protein S genes (genes 1 and 2). These genes are highly homologous at the DNA and protein level but they are expressed differentially. These genes will be analyzed by first determining the DNA sequences involved regulation of their expression. The effect of specific mutation of the protein S regulatory DNA on gene expression will be tested in developmental cells using fusions of these genes to the lacZ gene of E. coli. Expression of the gene fusions is conveniently monitored by the assay for Beta-galactosidase activity. The mutant genes will also be tested for their ability to serve as templates for transcription and to bind regulatory proteins in crude cellular extracts. Another approach to the study of these genes will be to isolate mutant M. xanthus strains which fail to express protein S gene 1 or gene 2 during development. Among these mutants will be strains which pleiotropically fail to express classes of developmental genes. These regulatory mutants will be identified by screening for properties such as the failure to express other developmental genes, or failure to undergo aggregation or sporulation. Analysis of mutant protein S genes and of regulatory mutant strains will provide insight into the mechanisms controlling developmental gene expression and multicellular fruiting body formation in M. xanthus.